Torsion springs have been utilized in a number of different applications; many of those springs have used rubber, urethane, or other elastomeric materials to achieve the action of a torsional spring or a rotary spring. One such device that utilizes rubber is described in Ballard U.S. Pat. No. 2,690,335. A somewhat more sophisticated elastomer torsion spring is disclosed in Kramer et al. U.S. Pat. No. 4,171,920. Specific applications for torsion springs are quite numerous; among others, they include vehicle shock absorbers, gate closers, and biasing devices, often called tensioners, for conveyor belt scrapers. Some can be set in increments to supply a given torsional force; such devices include the conveyor belt scraper biasing devices (tensioners) disclosed in Gordon U.S. Pat. No. 4,533,036 and Swinderman et al. U.S. Pat. No. 4,925,434. Another incrementally adjustable conveyor belt scraper tensioner, which uses a metal coil spring, is described in Mort U.S. Pat. No. 5,201,402. A continuously adjustable rotary bias device, suitable for use as a tensioner in a conveyor belt scraper, that uses a resilient elastomer member for the desired spring action, is described in Gordon U.S. Pat. No. 5,149,305.
A somewhat different torsion spring arrangement, particularly intended for use with a swinging hinged gate, is disclosed in Floehr U.S. Pat. No. 3,022,536. The Floehr device includes a means for adjustment of the spring force. Another torsional gate closer, employing a pre-stressed torsion bar, is described in Romberg U.S. Pat. No. 3,748,687.
Most known elastomer torsion spring devices, particularly those referred to above, have had provision for quite limited adjustment of the torsional restoration force of the device. The device of Gordon U.S. Pat. No. 5,149,305 adjusts a preset bias exerted by a tubular torsion spring having a fixed rate, but the actual torsional force or spring rate, per se, is not adjusted. For some applications this kind of adjustment may be inadequate; an elastomer torsion device in which the restoration force itself (torsional resistance) is adjustable over a broad range is more desirable.